6′-Sialyllactose [O—(N-acetyl-α-neuramionsyl)-(2→6)—O-β-D-galactopyranoyl-(1→4)-D-Glucose](hereinafter, referred to as 6SL) is an acidic oligosaccharide in which sialic acid is linked to lactose.
6SL is useful, for example, as a product, a raw material, an intermediate, or the like of health food, pharmaceuticals, cosmetics, and the like. 6SL is one of important oligosaccharides contained in human breast milk and is supposed to have a bioactivity such as a protective activity against infection with a virus or a bacterium, or an activity of lactic acid bacterial growth.
As a method for purifying 6SL, a method using a gel filtration column (Non-Patent Documents 1 and 2), a simulated moving-bed chromatographic separation device (Patent Document 1), or the like has been disclosed. Further, Patent Documents 2 to 4 describe that a crystal of 6SL salt was obtained, but do not describe the properties of the obtained crystals, and a method by which a crystal of 6SL salt can actually be obtained has not been known.